Caldera

A large basin-shaped volcanic depression with a diameter many times larger than included volcanic vents; may range from 2 to 50 km across. Commonly formed when magma is withdrawn or erupted from a shallow underground magma reservoir. The removal of large volumes of magma may result in loss of structural support for the overlying rock, thereby leading to collapse of the ground and formation of a large depression. Calderas are different from craters, which are smaller, circular depressions created primarily by explosive excavation of rock during eruptions.